From TactWiki
Overview
Station represents the role of an NPC in a town. Every Civic NPC available for Civic Diplomacy belongs to one of eight stations. Players must meet the minimum presence requirement to parley with Civic NPCs. The type of presence corresponds to the the NPC's station. An NPC's station, along with their race, generally determines the type of expressions used while parleying. Different city buffs (or levers) are available for each NPC station and conversation.
See the article on Civic NPCs for a list of NPCs by station in each town.
NPC Stations
Diplomacy Quests by Station